Table 3 Qualitative summary of the color changes during aging with explanation based on spectroscopy results
Pigment | Color changes in VIS aging* | Dye/Brightener degradation |
|---|---|---|
White | No change UV aging: slight decrease in fluorescence | Degradation of Fluorescent Brightener 184 only in UV aging as observed in Raman spectra |
Blue | Minimal darkening in color and in fluorescence UV aging: darkening in color and complete loss of fluorescence | Degradation of Coumarin 1 mainly in UV aging |
Green | Color Change to turquoise; fluorescence became brighter and then shifted to blue | Degradation of Solvent Yellow 172 Degradation products might fluoresce blue |
Lemon Yellow | Became greenish and lost its chroma; fluorescence shifted to blue | Degradation of Solvent Yellow 172 as observed in Raman spectra |
Golden Orange | Became yellow and lost its chroma; fluorescence shifted from orange over green to blue | Degradation of group R1 rhodamines followed by the degradation of Solvent Yellow 172 |
Brick Red | Became orange and lost its chroma; fluorescence shifted from red to blue | Degradation of rhodamines which is directly accompanied by the degradation of Solvent Yellow 172 |
Cyclamen Red | Became more reddish and lost its chroma; fluorescence shifted from red to blue | Degradation of rhodamines Absence of Solvent Yellow 172 leads to the final fluorescence from Fluorescent Brightener 184 |
Violet | Became pinkish and the chroma increased at the beginning and finally decreased; fluorescence became much brighter UV aging: rapid color change, characteristics similar to aging in VIS | High dye concentration led to quenching before aging Degradation of an unknown violet dye sensitive to VIS and UV |